On-demand type ink jet recording methods are known in which discharge ink droplets are discharged from a nozzle according to an image signal to form an image on a recording paper. In connection with the on-demand type ink jet recording method, a heating element type ink jet recording method and a piezoelectric element type ink jet recording method are known.
In the heating element type ink jet recording method, air bubbles are generated in ink by heat provided by a heat source in an ink flow channel. The ink pressed by the air bubbles is discharged from a nozzle.
In the piezoelectric element type ink jet recording method, a pressure change occurs in an ink chamber, where ink is stored, due to the deformation of a piezoelectric element. Thus the ink is discharged from a nozzle.
A piezoelectric element is an electromechanical conversion element, undergoes expansion or shear deformation when an electric field is applied thereto. Lead zirconate titanate is used as a representative piezoelectric element.
With respect to an ink jet head using a piezoelectric element, a configuration using a nozzle plate formed of a piezoelectric material is known. The nozzle plate of the ink jet head includes an actuator. The actuator includes, for example, a piezoelectric film having a nozzle for discharging ink, and a metal electrode film formed on both surfaces of the piezoelectric film surrounding the nozzle.
The ink jet head includes a pressure chamber that is connected to the nozzle. Ink enters the pressure chamber and the nozzle of the nozzle plate and forms a meniscus within the nozzle, and thus the ink is maintained within the nozzle. When a driving waveform (voltage) is applied to the two electrodes provided around the nozzle on either side of the piezoelectric film, an electric field in the same direction as a polarization direction is applied to the piezoelectric film through the electrodes. Thereby, the actuator expands and contracts in a direction perpendicular to the direction of the electric field. The nozzle plate deforms by virtue of the expansion and the contraction of the actuator. A pressure change occurs in the ink within the pressure chamber due to the deformation of the nozzle plate, and thus the ink within the nozzle is discharged.
When a nozzle plate is formed, film stress occurs. There is a concern that a uniform deformation of the nozzle plate through an actuator may be obstructed by the film stress of the nozzle plate. When the deformation of the nozzle plate becomes non-uniform, there is a concern that a discharge direction of ink may become unstable.